1. Field of the Invention
The present invention relates to a ceramic multilayer circuit board manufactured by baking several laminated green sheets, which respectively have wiring patterns thereon, and particularly relates to a ceramic multilayer circuit board suitable for holding electronic parts on a surface thereof.
2. Related Arts
A ceramic multilayer circuit board is generally manufactured by a green sheet lamination method using laminated green sheets. Specifically, first, via-holes are formed in the respective green sheets in a punching process and are filled with a tungsten paste or a molybdenum paste. Then, conductive layers are formed on the respective green sheets to form wiring patterns (inside wiring patterns) in a printing process using a paste such as a tungsten paste or a molybdenum paste as well. After performing the above-mentioned processes, a specific number of the green sheets are laminated and are hot-pressed to be united to each other. The united green sheets are cut into a specific shape, and then are baked at a specific temperature. Accordingly, the ceramic multilayer circuit board with a basic structure is obtained.
To mount an electronic parts such as a flip chip on the multilayer circuit board, a solder paste is previously applied to a mounting surface of the circuit board by a screen printing method using a print mask. In this case, however, it is difficult to apply the solder paste to a specific portion of the mounting surface with a uniform thickness. There is a case that the specific portion of the mounting surface has a part to which the solder paste is not applied. This results in deterioration of mounting reliability of the electronic part.
One of reasons why the solder paste cannot, be uniformly applied to the specific portion of the mounting surface is a warp locally generated on the circuit board, especially to raise a part of the mounting surface. The warp of the circuit board locally raising the mounting surface increases a pressure applied thereto by a squeegee in the printing process. As a result, the non-applied portion of the solder paste is produced. The warp further adversely affects the print mask to reduce a duration of life of the print mask.
On the other hand, in recent years, a flip chip having a plurality of bump electrodes is mounted on the circuit board to realize a high mounting density, so that the number of the bump electrodes on the circuit board is increased. To comply with the increase in number of the bump electrodes, each diameter and a bump pitch of the bump electrodes are decreased. This results in a decrease in a gap between the flip chip and the mounting surface of the circuit board. If the circuit board has the warp locally raising the mounting surface where the flip chip is mounted, the gap between the flip chip and the mounting surface of the circuit board is further decreased.
The gap between the flip chip and the circuit board is generally filled with a resin material containing inorganic filler such that the bump electrodes is not affected by thermal stress caused by a difference in thermal coefficient between the flip chip and the circuit board. When the resin material is supplied into the gap between the flip chip and the circuit board having the above-mentioned local warp, the warp prevents the inorganic filler from being uniformly distributed in the gap. As a result, the mounting reliability of the flip chip deteriorates.